The 15th annual Tribeca Film Festival kicked off fashionably with the premiere of Andrew Rossi’s “The First Monday in May,” a behind-the-scenes documentary about the mounting of an ambitious fashion exhibit at the Metropolitan Museum of Art and the museum’s annual star-studded Met Gala.

The film is an intimate and lively look at the highest aspirations of fashion, revealing everything from Anna Wintour fretting over seat assignments (Where to put Anne Hathaway?) to Rihanna’s eye-popping budget for performing at the ball.

The opening night, held Wednesday at the festival’s customary Westside outpost at the Borough of Manhattan Community College, drew an especially well-heeled crowd eager for a documentary antidote to “The Devil Wears Prada.” Among the fashion luminaries in attendance were Wintour, Vogue’s Grace Coddington and designer Zac Posen.

Rossi, a filmmaker who has profiled other New York institutions including The New York Times (“Page One”) and Le Cirque restaurant, said Tribeca was a fitting place to unveil “The First Monday in May.”

“The Metropolitan Museum and Vogue are tremendous powerhouses in the creative life of New York City, certainly occupying more of the uptown world,” Rossi said. “So Tribeca, which is a festival founded to celebrate the arts in New York, for them to embrace the film and present it as opening night is a great honor.”

This year’s Tribeca bows amid a controversy. When Tribeca programmed a screening of an anti-vaccination documentary, “Vaxxed,” by the discredited British doctor Andrew Wakefield, it prompted an uproar from science researchers and filmmakers.

“I think the movie is something that people should see,” he told the “Today” show in an unusually passionate interview.

De Niro expressed bitter disappointment in filmmakers who threatened to pull out from the festival over the film, and he promised to find out who had.

Considerable scientific research has found no connection between vaccinations and autism, and the Centers for Disease Control and Prevention has emphatically stated that “vaccines do not cause autism.” But De Niro insisted on “Today”: “There’s something there that people aren’t addressing.”

The ordeal has threatened to overshadow one of Tribeca’s more ambitious editions. Over the next 12 days, the festival has some 100 films to unveil, a robust multimedia program including numerous virtual reality exhibits, a host of television show premieres and numerous staged celebrity conversations.

“At Tribeca we keep an eye on tomorrow,” festival co-founder Jane Rosenthal at a press luncheon Wednesday. “We love stories in just about any form, from a Harold Lloyd silent film captured on a 35 millimeter hand-cranked camera to a virtual reality adventure shot with multiple GoPros to a video game in which the viewer is in the driver seat determining how the narrative unfolds.”

“The First Monday in May” is a fitting opener. It mostly follows Met Costume Institute curator Andrew Bolton as he frantically puts together what would be a blockbuster exhibit, “China: Through the Looking Glass,” and strives for equal standing amid the Met’s more traditional art forms.

But for many, the film will be most sought out for its rare look inside Wintour’s annual Met ball, one of the biggest nights in fashion. The Hollywood Reporter called it “catnip for fashionistas.”

Rossi said he viewed his film, shot with what he called “a crackling cinema verite approach,” a kind of hybrid between the 2009 Vogue documentary “The September Issue” and Frederick Wiseman’s 2014 portrait of the exalted London museum “National Gallery.”

The biggest challenge, Rossi said, wasn’t getting access to the many personalities of “The First Monday in May,” including Baz Luhrmann, Wong Kar Wai and Wintour. More difficult, he said, was getting the Met to allow him and his cameramen freedom to follow their subjects in the museum’s hallowed halls.

“It was absolutely necessary to say, ‘We can’t be on a tripod the whole time,'” Rossi said.